Process for producing elastic core yarns



Nov. 12, 1968 E ORD, JR ET AL 3,410,080

PROCESS FOR PRODUCING ELASTIC CORE YARNS Filed Aug. 7, 1963 PROCESS FOR PRODUCING ELASTIC I CORE YARNS Edwin L. Lord, 'Jr., and Albert Stewart Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, -Wilmington, Del., a corporation of Delaware Filed Aug. 7, 1963, Ser. No. 300,552 6 Claims. (Cl. 57-163) This invention relates to the preparation of elastic yarns and particularly to the preparation of composite elastic. yarns wherein the elastic component is concentrated in the .core of the yarn structure.

It is well known in the art to combine continuous filament elastic yarn, which may be either rubber or a synthetic elastomeric yarn, with inelastic fibers by any of several procedures. In one procedure, the continuous filament elastic core is wrapped with one or more layers of inelastic yarn, which may be either a continuous filament yarn or a spun yarn, on a conventional twisting machine or on a hollow spindle covering machine well known in the art for this purpose. In another procedure, the continuous filament elastic yarn is combined with roving made of inelastic staple fibers in the drafting zone of a conventional spinning frame. The composite yarns produced in this way are widely known as core-spun elastic yarns. The basic method and numerous variants thereof are disclosed in a number of patents, among which may be mentioned by way of example US. 2,024,156, US. 3,017,740, and US. 3,038,295.

For reasons of economy, in making any of the types of composite elastic yarns based on a continuous filament elastic member, whether by wrapping on a hollow spindle machine, by simple twisting on a twisting frame, or by core-spinning, it is desirable to combine the elastic yarn with only one end of inelastic yarn, either continuous filament or spun yarn It frequently occurs, however, that a single end of inelastic fiber does not completely cover the elastic yarn element. Although this condition can be tolerated for many uses, it is usually not desirable that the elastic yarn appear exposed on the face of the fabrics made from the composite yarn. This undesirable elfect, commonly known as grinning, is accentuated if there is a pronounced color difference between the elastic and inelastic components of the yarn. This will be true when the inelastic fibers are dyed and the elastic yarn is not, or if both elastic and inelastic fibers are undyed but the elastic yarn has a substantially different color from the inelastic fibers, as will commonly be the case, for eX- ample, with natural rubber. In the past, when it has been absolutely essential that the elastic yarn not be apparent on the surface of the fabric, the usual solution to the problem has been the expensive expedient of providing two or more covering layers of inelastic fibers. Numerous attempts have been made with varying success to provide a composite elastic yarn with a single inelastic element wherein the elastic member is fully covered.

It is also known to prepare elastic yarns from blends of elastic and inelastic staple fibers by spinning according to conventional spun yarn manufacturing procedures, as taught in U .5. 3,007,227. Because the elastic elements of these yarns are discontinuous, control of the effective utilization of their elastic characteristics in the composite yarn is more difiicult than in the case of yarn based on continuous filament elastic yarns. Likewise, because the elastic elements in the staple blend yarns are discontinuous, they are free to migrate to the surface of the yarn structure, where, after a period of wear, they may contribute to unsightly appearance of the fabric surface.

It is an object of this invention to provide a process for preparing elastic yarn of either the corespun or staple nited States Patent 3,410,080 Patented Nov. 12, 1968 blend variety having improved aesthetic and functional characteristics by virtue of the elastic components of such yarns being concentrated in the core of the yarn structure. It is another object of this invention to provide a process for preparing staple blend elastic yarn wherein improved control is maintained over the elastic elements in the yarn structure. It is a further object of this inven tion to provide a process for preparing staple blend elastic yarns wherein migration of the discontinuous elastic elements within the yarn structure is effectively prevented. It is still another object of this invention to provide a. process for preparing composite elastic yarns wherein substantially complete cover of the elastic element is achieved with only one inelastic component.

In general, the objects of this invention are achieved by an improvement in a conventional process for preparing composite elastic yarns in which an elastic component is tensioned or stretched to substantially increase its length, a roving of staple fibers is drafted, and the core and roving are gathered and twisted to form the composite yarn. The improvement comprises passing the tensioned core and the drafted roving into the nip of a pair of forwarding rolls in a side-by-side relationship, The core is displaced from the center of the roving in a direction opposite to the direction of the desired twist. If a Z-twist is desired, the core is positioned to the left of the roving as it enters the forwarding rolls. Alternatively, if an S- twist is desired, the core is positioned to the right of the roving. Preferably, the roving and core are positioned in contiguous relationship. While a small amount of separation can be tolerated, separation greater than about oneeighth inch will result in undesirable loss of cover of the core by the roving.

The invention will be further described by reference to the accompanying drawing, in which:

FIGURE 1 is a diagrammatic view of a spinning frame having auxiliary tension and feed means useful in the manufacture of composite elastic yarns; and

FIGURES 2 and 3 are diagrammatic views showing the positions of the core and roving as they pass between the front rolls of the spinning frame.

Referring now to FIG. 1, a roving 10 is withdrawn from bobbin 12 and passed over guide bar 14 to the draft zone of a spinning frame where it passes between top and bottom back rolls 16 and 16. The roving is then passed between drafting aprons 18 and 18' which are supported by top rolls 20 and 22 and bottom rolls 20' and 22'. From the drafting aprons, the roving is guided into the nip formed by top front roll 24 and bottom front roll 26.

Simultaneously with the drafting of roving 10, elastic core yarn 28 is withdrawn from package 30 which is cradled between feed rolls 32 and 34. The core yarn 28 is passed from feed rolls 32 and 34 over tubular roll 38 and into the nip formed by top front roll 24 and bottom front roll 26. Positioning of the core yarn 28 relative to roving 10 may be achieved by guides, not shown, between roll 38 and the nip formed by the front rolls 24 and 26.

After roving 10 and elastic core yarn 28 leave the nip formed by the front rolls, they are passed through guide 36 to a conventional ring and traveler Winding device 40 where they are wound as a composite yarn 42 onto a bobbin 44.

In order to provide accurate control of the tensioning and drafting of the elements of the composite yarn prepared by the process of this invention, the elastic core tensioning and feed means is driven directly from front roll shaft 25. A conventional spinning frame may be readily adapted to drive the tensioning and feed means in this manner by merely attaching a split sprocket assembly 27 to shaft 25. Power may be transmitted from sprocket 3 27 to gear 29 by means of a chain 31. Rolls 38, 32 and 34 may likewise be driven by chains 33, 35 and 37, respectively.

The various elements of the apparatus may be driven at the desired rates of speed by appropriate selection of gear ratios. In general, it has been found desirable in the manufacture of elastic core composite yarns to drive roll 38 at the same linear surface speed as that of front rolls 24 and 26. Feed rolls 32 and 34 are: driven at substantially slower speeds, thus stretching core yarn 28 as it is passed to the nip of the front rolls. This stretch will usually be on the order of two to six times the original length of the elastic core yarn. It may be desirable, however, to use either higher or lower stretch ratios.

In preparing yarns by the process of the present invention when a Zrtwist is desired, FIG. 2 illustrates the relative positioning of the elements, core yarn 28 and roving 10, as they pass between front rolls 24 and 26, FIG. 3 shows the arrangement of core yarn 28 and roving 10 when an S-twist is to be imparted. The direction of twist used herein is that defined at page in the book by Truslow, N. A., Handbook of Twisting, Clark Publishing Co., Charlotte, NC, 1957. When the elastic core element is a continuous filament elastic yarn, it may be introduced behind the front rolls in the manner described in U.S. Patents 3,017,740 and 3,038,295. Alternatively, an elastic roving prepared from a blend of elastic and inelastic staple fibers as taught in U.S. Patent 3,007,227, may be used. In the latter case, the elastic core element will have passed through the draft zone of a spinning frame. in a conventional manner and can be maintained in spaced parallel alignment with inelastic roving until the two rovings pass through the front rolls and are combined.

The following examples illustrate the necessity for maintaining a side-by-side relationship of the core and covering as the two emerge from the nip of the front rolls. It will be seen that while a small amount of separation of the two elements can be tolerated, it is critical that the separation be not greater than one-eighth inch. In the examples, the terms left and right refer to the positions of the elements as viewed as they emerge from the front rolls of the spinning frame.

Example I A composite yarn having an inelastic covering and an elastic core is prepared using apparatus of the type illustrated in FIGURE 1. A 70-denier (7.78 tex) continuous filament spandex yarn of the type described in U.S. Patent 3,039,895 is used as the core. This yarn is given 300% stretch before it is introduced into the nip of the front rolls. A. 1.0 hank (591 tex) roving with 0.67 turn per inch Z-twist is prepared from 64-70s grade wool. The roving is dyed black. In spinning the composite yarn, the roving is given a draft of 19.2 and combined with the elastic core to form a composite yarn equivalent to /1 c.c. (29.6 tex) with 18 t.p.i. Z-twist. In the yarn spinning operation, rings having a diameter of 2.5 inches and a No. 19 traveler are used with a spindle speed of 6100 rpm.

Three different yarns are prepared with the elastic core being guided into the front rolls so as to emerge from the rolls in each of three different positions relative to the inelastic roving.

The first sample is prepared by spacing the elastic core between 0.125 and 0.25 inch to the left of the left edge of the inelastic roving. Inspection of the composite yarn reveals severe grinning, i.e., incomplete covering of the core.

The second sample'is prepared by guiding the elastic core into the front rolls precisely along the left edge of the inelastic roving. Upon inspection, it is found that the resulting composite yarn is a yarn with excellent covering of the core element.

In preparing the third sample, the elastic core is spaced between 0.125 and 0.25 inch to the right ofthe right edge of the inelastic roving. The resulting composite yarn is of poor quality showing incomplete covering of the core.

Additional samples of composite yarns were prepared as described above except that the yarns were spun with 14 and 16 turns per inch Z-twist. The difference in turns per inch twist did not affect the results obtained above.

Example II The procedure described in Example I is repeated in preparing composite yarns except that the elastic core is prepared from a blend of elastic and inelastic fibers as described in U.S. 3,007,227. A spandex staple fiber of 6-denier per filament (0.67 tex per filament) having a length of 2.75 inches is prepared by cutting a spandex tow of the type described in U.S. 3,077,006. The spandex staple fiber is blended with commercially available polyethylene terephthalate staple fiber having a denier per filament of 2.25 (0.25 tex) and a length of 3.5 inches to form a 2.0 bank (295 tex) elastic roving with 0.46 turn per inch Z-twist. The elastic roving contains polyethylene terephthalate fibers and 10% spandex fibers. An inelastic 2.0 bank (295 tex) roving having 0.445 turn per inch Z-twist is prepared from the same polyethylene terephthalate staple fiber.

The two rovings are double creeled on a spinning frame, i.e., one end of both the elastic and inelastic roving is creeled per spindle. The two rovings are guided into the nip of the front rolls to produce a series of composite yarn samples which will be described later herein. Each of the composite yarns prepared is a 20/1 c.c. (29.6 tex), 18.7 turns per inch Z-twist yarn, and is spun using rings having a diameter of 2.5 inches with a No. 21 traveler at a spindle speed of 6500 rpm.

The first composite yarn is prepared by positioning the elastic roving 0.5 inch to the left of the left edge of the inelastic roving. Inspection of the composite yarn reveals that the yarn is unsatisfactory in that the core element is poorly covered.

The second sample is prepared by positioning the elastic roving 0.25 inch to the left of the left edge of the inelastic roving. Inspection of this yarn reveals a better covering of the core than observed for the first sample; however, both properties are considered to be marginal.

The third sample is prepared by positioning the elastic roving precisely at the left edge of the inelastic roving. A good yarn, exhibiting excellent cover, is provided.

The fourth sample is prepared by positioning the elastic roving precisely at the right edge of the inelastic roving. Poor cover of the elastic yarn is observed.

In preparing the fifth sample, the elastic roving is positioned 0.25 inch to the right of the right edge of the inelastic roving. Poor cover of the elastic roving is observed.

The sixth sample is prepared by positioning the elastic roving 0.5 inch to the right of the right edge of the inelastic roving. The cover of the composite yarn is poor.

When the position of the components is reversed and an S-twist is imparted to the components, results similar to those described in each of the six instances are observed.

Certain modifications can be made in the process which has been described herein. When using a conventional spinning frame to prepare composite yarns, a more effective cover for the elastic core can generally be obtained if the roving which is to serve as the cover is brought into contact with the surface of the bottom front roll slightly in advance of the nip formed by the front rolls. Contact with the roll tends to spread the roving into a flat, thin ribbon enhancing its ability to wrap around the core and provide an effective cover.

The apparatus which has been illustrated may be modified in a number of respects. Various feed and tensioning devices as well as guides may be used. The feeding of a plurality of core and covering elements may be readily accomplished by the adition of elastic core feeding and tensioning means for each position on a conventional spinning frame. It will be apparent to those skilled in the art that the core component may be a stretch yarn prepared from inelastic fibers.

The composite elastic yarns made according to this invention may be employed in any of the multitude of uses where elastic yarns find application. They are particularly advantageous in apparel fabrics, and especially dyed fabrics, where the substantially complete cover afforded by this invention overcomes the long-standing problem of grinning and where the concentration of elastic elements in the core of the yarn bundle overcomes the problem of migration of elastic filaments to the surface of the fabric. However, their usefulness is not limited to such apparel fabrics.

The invention has been described particularly with reference to production of core-spun and staple blend yarns on conventional spinning frames, but it will be understood that the principle of the invention may be applied whenever an elastic member is to be covered with a single inelastic member in a twisting operation. The principle of the invention, therefore, has wide application in the art and, accordingly, the invention is intended to be limited only by the scope of the appended claims.

We claim:

1. In a method for producing a composite elastic yarn comprising the steps of tensioning an elastic core to substantially increase its length, drafting a roving of staple fibers, and thereafter gathering and twisting the elastic core and the roving together whereby said elastic core is covered by said roving; the improvement which comprises passing the tensioned core and the drafted roving into the nip of a pair of forwarding rolls in a side-by-side relationship for direct advancement to a windup, said core being displaced from the center of said roving in a direction opposite to the direction of twist, the distance between said core and said roving being not greater than about one-eighth inch.

2. The process of claim 1 wherein said elastic core is a continuous elastic filament.

3. The process of claim 1 wherein said elastic core is comprised of a blend of elastic and inelastic staple fibers.

4. Theprocess of claim 1 wherein said core and said roving are passed through said forwarding rolls in contiguous relationship.

5. The process of claim 4 wherein said roving is spread to form a fiat thin ribbon by bringing it in contact with the surface of one of said rolls in advance of the nip.

6. In a method for producing a composite elastic yarn comprising the steps of tensioning an elastic core to substantially increase its length, drafting a roving of staple fibers, and thereafter gathering and twisting the elastic core and the roving together whereby said elastic core is covered by said roving; the improvement which comprises passing the tensioned core and the drafted roving into the nip of a pair of forwarding rolls with the core being positioned at an edge of the roving for direct advancement to a Windup, said core being displaced from the center of said roving in a direction opposite to the direction of twisting.

References Cited UNITED STATES PATENTS 420,669 2/1890 Whitehead 57l2 1,198,997 9/1916 Cunningham 57--12 XR 1,286,311 12/1918 Heathcock 57-12 XR 2,024,156 12/1935 Foster 57-152 2,076,270 4/1937 Harris 57-163 2,901,884 9/1959 Weinberger et al. 57-144 JOHN PETRAKES, Primary Examiner. 

1. IN A METHOD FOR PRODUCING A COMPOSITE ELASTIC YARN COMPRISING THE STEPS OF TENSIONING AN ELASTIC CORE TO SUBSTANTIALLY INCREASE ITS LENGTH, DRAFTING A ROVING OF STAPLE FIBERS, AND THEREAFTER GATHERING AND TWISTING THE ELASTIC CORE AND THE ROVING TOGETHER WHEREBY SAID ELASTIC CORE IS COVERED BY SAID ROVING; THE IMPROVEMENT WHICH COMPRISES PASSING THE TENSIONED CORE AND THE DRAFTED ROVING INTO THE NIP OF A PAIR OF FORWARDING ROLLS IN A 